Process of making pressed board products



Patented Sept. 17, 1940 PROCESS OF MAKING PRESSED BOARD PRODUCTS Harry K. Linzell, Greenville, Miss., assignor to United States Gypsum Company, Chicago, 111., a corporation of Illinois No Drawing. Application July 3, 1935, Serial No. 29,733

4 Claims.

The present invention relates to a pressed board product and the process of its manufacture. The primary object of the invention is the production of a hard, dense, coherent article of 5 synthetic lumber, usually in the form of boards or slabs which may be used for building purposes, interlor decoration, panel boards, and the like.

One of the objects of the invention is the procellulosic fibers or cellulosic and ligneous fibers in admixture with each other together with a comparatively small amount of a binder such as a hardenable oil in conjunction with auxiliary binders formed as a. result of partial pyrolytic decomposition of the cellulosic or ligneous fibers. A further object of the invention is to produce synthetic lumber by a process which involves the fibration of a ligneous substance such as wood, or various plants-either by a mechanical or a chemical process, preferably the former, followed by the reassembly of the resulting fibers into a coherent mat or slab with the simultaneous incorporation with the fibers of a relatively small amount of a hardenable oil. After the incorporation of the oil, the board may be subjected to heat and pressure within definite ranges, as will be supplement the natural binders contained inthe material. The presence of the oil further acts to bind the material closely together while at the same time endowing it with properties of toughness and resilience.

The oils used may be of any suitable origin and preferably comprise such oils as linseed oil. Perilla oil, China-wood or tung oil, soya bean oil, fish oils, menhaden oil, oil of Java olives, and other oils which have the property of hardening by drying, usually with the formation of what is technically known as linoxyn. The size used upon the fibers may consist of the ordinary rosin size used in the form of a rosin soap, or may be a resin which is capable of saponification or emulsification, although it is understood that other water-proofing materials in the nature of duction of a board composed substantially of waxes such as paraffin wax, carnauba wax,-ceresin wax, ozocerite wax; montari'wax, and the like, may be used.

Broadly speaking, the present process comprises the fibration of ligneous material, although this does not exclude the use of fibers which have been chemically liberated from wood. Wood that has been merely mechanicallyfibrated forms the preferred embodiment of the invention. Assuming. that the manufacture is to proceed on the basis of the use of ground wood; which is usually ground in the presence of water by means of theusual pulp stones, the resulting pulp suspension is run into a suitable tank provided. with an agitator and while therein is treated with, for example, rosin size in an amount approximately 1% to 2% of the Weight of the fibers. At the same time there is ruri into the tank, preferably in the form of an emulsion, but not necessarily so, up to 10% of ahardenable oil as, for example, linseed oil, Perilla oil, tung or China-wood oil, soya bean oil, fish oils, and the like. If thorough agitation is used, the previous emulsification of the oil is not absolutely essential, the main object being to obtain as thorough intermixing of the oil, resin size andfibers as can reasonably be attained. After the oiland fibers have been mixed in the said tank, a sufiicient quantity of a precipiv tant such as alum or aluminum sulfate is added to decompose the rosin soap size, with the formation-in the usual manner-of an insoluble precipitate which deposits itself upon the fibers, at the same time carrying down with it the oil that has been added to the mixture. The result of these treatments is that the resin now in the form of its aluminum complex and the oil'are both deposited upon the fibers. The resultant suspension'of sized and oiled fibers is now transferred'to a suitable board-forming machine such as a Fourdrinier or Oliver board former, or other mechanical equivalent device, upon which it isformed into a wet mat. This mat is then slightly compacted by being passed between squeeze rollers, all in the manner well known in this art, whereupon the resultant damp mats are transferred to a drier wherein they are dried at a temperature above 212 F., with the removal of all or substantially all of the moisture therein contained. During this drying there takes place a hardening of the oil, with the formation of linoxyn. As the time of hardening and formation of linoxyn varies with the type of oil-used, it may be advisable to store the dry boards for from a day or so to a few weeks, depending upon the rate at which the various oils which may be emssh ' possible to add to the oil a small amount of the ployed oxidize. It has been found that excellent results are obtained when the oil is dried to the state where it becomes merely plastic when subjected to heat and pressure. In order to enhance the hardening of the oil, itwill, of course, be

well known driers such as manganese, cobalt, or lead compounds, which are known in thepaint and varnish industry; and in claiming oilsherein it is to be understood that these may include such driers. In place of the rosin'size, or .conjointly therewith, there may also be used a small percentage, say 2%, of the aforementioned parafiin or waxes, these being incorporated preferably in either finely divided or emulsified form, although their use in the formof saponification products or soaps is not to be excluded. 1

Assuming for the purposes of the present description that a board having two plane fiat surfaces is to be made, the board is first thoroughly relieved of all the therein contained vaporizable matter or moisture, and the board is then placed between heated surfaces, such for example as the platens of a hydraulic press, whereupon impacting pressure is applied to said boards of from' 500 to 3000 pounds per square inch for a period of from one minute up to one hour at a temperature range of from 350 F. upward, but short of thepoint of active development of carbon for the materials. The ignition point of wood is about 527 F. As a result of the applied pressure there is brought about a consolidation of the board while at the same time the heat tends to decompose the cellulosic and ligneous constituents thereof, with the autogenous formation of resinous and tarry condensation products which act as auxiliary binders and serve to bind the fibers of the board together into a strong and coherent mass. The function of the oil and waterproofing agents is greatly toenhance the resistance of the product to the inter-penetration of liquids such as water, thus producing a dense water-repellent and water-resistant board.

If, on the contrary, the mats have been stored for some time in order to permit hardening of the oils, the boards. will then contain hygroscopic moisture which they have picked up from the atmosphere. Boards containing such moisture can be pressed if there be interposed between at least one surface thereof and the heated platens some foraminous material such as a screen, in order to permit the escape of moisture which is converted into steam because of the heat imparted to the mats by their contact with the surfaces of the platens.

In order to prevent possible difficulties resulting from the adhesion of the boards to the platens of the press, it is preferable to interpose between the boards and the platens heat-conducting caul plates of oxidized metal or sheets coated with enamel or a glass-like composition. In stating the temperatures used in the present process, it is understood that these temperatures are measured at the surface of the metallic heatconducting bodies that are in contact with the boards. Of course, if the platens themselves are of oxidized metal or are coated with enamel or other glass-like composition, such intermediate sheets may then be dispensed with. At anyrate, the temperatures mentioned are the temperatures in contact with the board and not the temperatures of the interior of the platens themselves.

As a specific embodiment of the present invention, it may be stated that if a board sized with.

rosin and containing a hardenable oil is to be pressed, the temperature is preferably above 350 but below the point of active carbon formation.

Instead-of forming the board wet, it is possible -to proceed by first producing dry fibrated wood,

as by grinding the same. The thus produced fibers are then mechanically mixed with a small amount of the above-mentioned oily substances to form fibers having these substances adhering thereto. The thus treated fibers are then stored, either hot or cold, to allow the added oil to harden. .Thereupon the fibers are mechanically made into a mat, as by blowing them with an air current onto a foraminous surface while'applying suction to the latter. This mat-is then laid onto the platens or the oxidized or enamelled caul plates, and pressed in the manner already described.

of but a few minutes while at the lower end it may extend from one-half to one hour.

A somewhat similar effect is noticed in the case of pressures, and as a general rule the higher the pressure the shorter may be the pressing time, in order to secure a board of approximately the same density, although it is not to be understood that the relationship of the pressure to the time is the same as that of the temperature to the time. Thus, if both a high pressure and a high temperature are used, the resultant product will be very hard and very dense and may be pressed in a comparatively short time, whilst on the contrary, if the pressure is light and the temperature is low, the pressing time must be correspondingly lengthened, but in the latter case the density will be lower.

When pressing a board, a temperature between 425 F. and 475 F. is suitable.

One of the advantages in interposing an oxidized metal caul plate or an enamelled or glasslined caul plate between the boards being pressed and the platens is that such plates require little or no greasing or oiling, as they are naturally endowed with a tendency to obviate the sticking of the boards. This greatly simplifies manipulation and greatly facilitates rapid and economical manufacturing operations.

In carrying-the present invention into commercial practice, it has been found that there are distinct advantages in applying the impacting pressures in distinct stages'or intervals, the pressure being either the same at each period or difierent in each of the periods, as will presently be explained. In any'event, there is a release of pressure between the individual impactions. For example, sheets of insulating board completely relieved of their moisture, are placed on caul plates and the assembly inserted between the platens of a hydraulic press. The temperature as measured at the surface of these platens may be, for example, between 450 F. and 455 F. The press is then operated so as to bring the platens into contact with the boards, but without the application of any substantial pressure, for the purpose of heating the surface of the boards to about the temperature of the platens. This usually takes from one to three minutes. During this time, which can conveniently be termed the toasting period, the board surface will have acquired a temperature sumciently high so as to prevent the adhesion of the boards to the caul plates. The pressure is then applied for a period of from two to three minutes, whereupon it is gradually released and the platens allowed to lift slightly oif the boards for the purpose of allowing the escape of the accumulated gases and vapors. A bluish acrid smoke will beseen to rise from the boards and pass out between the platens. The pressure is then again applied for a further period of from.

two to three minutes, whereupon it is again released in the same manner as already described. The pressure is then once more applied, and at the end of another period of two or three minutes the pressure is finally released and the press opened. Thereupon the boards are quickly removed from the press and immediately subjected to a strong blast of air, preferably but not necessarily heated, to remove as much as possible of the smoke and gases'from the freshly formed boards. This is done in order to remove the somewhat acrid odor which would otherwise ad-' here to the boards. The boards may then be passed through a passageway in which they are subjected to a blast or current of cool air in order to relieve them of heat and allow them to assume room temperature without warping.

It has been found particularly advantageous to change the pressure during the various times that it is applied, this pressure either increasing or, in some instances, being lowered. For exampie, when making a hardened board inch thick and of a density of from 65 to '75 pounds per cubic foot and working at a temperature of 450 to 455 F., measured-at the surface of the platens,

the cycle may be substantially as follows: The board is subjected to the toasting operation at a pressure of not exceeding 50 pounds for a period of one minute, whereupon the pressure is released momentarily to allow the escape of the initial amount of smoke and gases formed. The

pressure on the boards is then raised to 400 pounds per square inch for a period of two minutes, whereupon it is released and the platens lifted clear of the boards. The pressure is then applied to the extent of 800 pounds per square inch and kept on for a period of two and onehalf minutes, whereupon it is again released and the platens lifted from the board. There then follows a final application of pressure on the order of 1200 pounds per square inch for a period of three minutes, at the end of which time the pressure is released, the press opened and the boards removed. The total pressing time counting from the moment the boards enter the press, and therefore including the toasting period of one minute,'is thus eight and one-half minutes.

As an example of the production of 55 inch hard board at 450 to 455 F. and having a. density of 65 to 70 per cubic foot, it may be stated that the entire cycle is somewhat longer, namely, about ten and one-half minutes, because of the fact that A inch board is 50% thickerthan inch board and that therefore the mass of material is 150% of that of the inch board. Inasmuch as the heat is abstracted from the surface of the board bythe loose-textured interior, it takes a little longer to get the surface of the board up to the platen temperatures, which makes it necessary slightly to increase the toasting period in this case 50%. Thus, in making the inch board, three intermediate pressure releases and the final pressure release, and three stages of pressure application respectively of 400, 800 and 1200 pounds per square inch, these periods being 3, 3 and 3 minutes respectively, are employed. The totaltime,

counting from the moment that the board enters the press and including the 1 /2 minute toasting period at less than 50 pounds pressure, is therefore 10 minutes.

In the manufacture of inch hard board at 450 to 455 F., the cycle is somewhat different,

The toasting period in this case at less than 50 pounds pressure is 2. minutes. The first application of pressure for a period of 2 minutesis 400 pounds, followed by two separate applications of pressure of 3 minutes each at 800 pounds, and

finally application of 1200 pounds pressure for 3 minutes, or a total of 14 minutes, counting from the time. the board enters the press.

Alternatively, in making inch hardboard of a density'of 65 to 70 pounds per cubic foot, at 450 to 455 F., the applications of pressure may all be of the same degree, viz., 1000 pounds. Thus the initial toasting period may be one minute,

followed by release of pressure and lifting of the platens from the boards, whereupon pressure of 1000 pounds is applied for 1 minutes, followed by pressure release and lifting of the platens just as previously described. The pressure is then again raised to 1000 pounds for 2 minutes, again released and then once more raised to 1000 pounds per square inch for a period of 2 minutes, whereupon the pressure is released and the press is opened. The total time, therefore, including the toasting period, is 7 minutes. When operating in this manner, however, the results are not as completely satisfactory as they are when working in accordance with the conditions where there are increments in pressure, for it appears that the development of the smoke and gases tends to the formation of a fiber board which shows a slight inclination toward blistering or laminating and also has a greater tendency to stick to the caul plates than when the pressure is applied in increments. It will be noticed, however, that the cycle is 1 minutes shorter and the highest pressure is 200 pounds less, that is, 1000 pounds instead of 1200 pounds.-

Still another way of operating, when making of to pounds per cubic foot, is as follows:

When working in accordance with the following conditions, the tendency of the board to laminate is very slight. In this type of cycle there is the usual toasting period of 1% minutes with a pressure of less than 50 pounds, followed by a pressure release and lifting of the platens from the board, whereupon a higher pressure of 1500 pounds per square inch is applied for a period of 1 minutes. The pressure is then released and the platens merely placed in contact with the boards, just as during the toastin period, and held that way for 4 minutes at a pressure of less than 50 pounds. During this prolonged second toasting period an opportunity is given for full d velopment of the desired quota of resupon the pressure is again applied to the full 1500 pounds for a period of 3 minutes. During this latter period the resins formed during the 4-minute toasting period, together with such additional resins as form during the second compression stage, are set and the board is given its final hardness. The total pressing time, including the initial toasting, is thus 10 minutes.

when working in a this manner, but

" temperature say from 462. to 464 E, the total time-cycle could easily be reduced to 7 minutes by shortening the intermediate toasting stage as well as the compression stages, as will be readily understood from what has been said above.

,It is also possible, although not as advantageous, to work at a lower temperature-such as 400- F., butin that case the time cycle is very greatly increased. This increase. in time cycle. however,- is compensated for by other advan-- a tages, viz.,-that less pressure need be carried on the boiler that furnishes the high pressure steam for heating the platens'and also that the skill ofthe press-operator need not be of ashighorder, nor need the cycles be so slavishly adhered 13 minutes, respectively, making a total time,

including the toasting, of 60 minutes; It will be obvious .that at 400 F. these intermediate cycles may be shifted about as to time without seriously interfering with the successful operation of the process. Furthermore, a variation in the total time of 10% in either direction would make very little difierence. Where a -stage press, for example, is used and there is but one operator, it is quite possible that the same operator could thus handle two presses, making twenty boards at a time, having time to attend to both of them without interfering with the proper. carrying out of his duties.

The manufacture of what may be called a semi-hard board, having a density of from 39 to 50 pounds per cubic foot, which is made by using stops to prevent the travel of the platens beyond the limits thereof, is about as follows: The stops are V inch thick, so that the board will under no circumstances be thinner than $4, inch. The pressing cycle is somewhat different. The initial toasting period is one minute. There is then an application of pressure of 250 pounds for 2 minutes, followed by the usual pressure release, followed bya cycle of 500 pounds pressure for 3 minutes, which sufiices to compress the board up to the limits of the stops, whereupon the pressure is released and the platens lifted as usual. The final application of pressure need therefore be only 250 pounds, because there would be no object in applyingany greater pressure than would be necessary to bring the reexpansion of the board above the limits of the stops. The total cycle in that particular example is 9 minutes; Obviously, the initial toasting may be carried out-under the full pressure of the press.

The boards produced by the; present process have a high modulus of rupture, have low water absorption and a pleasing and smooth polished surface. The fibers therein are consolidated to- V and the like. The inherent water-resistance and bonding-powers of these autogenously produced binders isfurther enhanced by the simultaneous presence of the hardened oils and the rosin size, which tends to plasticize the autogenously proaucea inqeris. It will be notedthat the amount of rosin sizeandoils is relatively small, and unless the temperaturesjwere within the range 'fore, the cooperation of the autogenously formed binders with the added oils which mutually contributes to the high degree of water resistance, lack of water absorption and final'strength. of

the products made in accordance, with the present invention. 1

Applicant is aware of the fact that waxes, oils and sizes have been used in the past for the purpose of enhancing the water resistance of fibrous products, but he is not aware that the autogenous development ofresins and condensation products conjointly with the use of hardened oils has ever been used before and therefore considers this as a distinct step in advance and as forming one of the essential elements of his present invention, for whichhe claims:

1. The process of forming ahard, dense, consolidated product consisting essentially of cellulosic and ligneous fibers in an interlaced condition, which comprises precipitating upon said fibers a metallic resinate and a drying oil while said fibers are suspended in a liquid, separating said fibers from said liquid to form a coherent loslc fibers.

2. The process'of consolidating ligneous cellulosic material into a dense, compact, coherent board or slab which comprises thesteps of mixing such material with a drying oil, forming the material into a coherent but pervious mat, removing the moisture from said mat and oxidizing the drying oil to a sufiicient extent to cause it to become dry. and thereafter pressing the resultant mat at a pressure of from 500 to 3000 pounds per square inch at a temperature of at least 350 F. but short of a temperature high enoughto cause development of carbon.

3. The process of consolidating ligneous cellulosic material into a dense, compact, coherent;

board or slab which comprises the steps of mixing said material with waterproofingmaterial and "a drying oil, forming the resultant mixture into a coherent but pervious mat, removing'the moisture" from said mat and subjecting the-same to oxidizing conditions for a time sufflcient to effect the oxidation of said drying oil so as to cause it to become dry and thereafterpresslngthe resultant mat at a temperature of at least 850 F.

but short of a temperature-high enough to cause development of carbon.

4; The process of forming a hard, dense, consolidated lignocellulosic product which comprises fibrating lignocellulosic material so as to yield a mixture of cellulosic and ligneous fiber precipitating upon said fibers a waterproofing material and a drying oil, forming the thus treated fibers into a coherent mat, subjecting said mat to drying and" oxidizing conditions so as to remove the moisture therefrom and to oxidize said drying oil 350 F. but short of a temperature high enough so that the same becomes dry, and thereupon to cause development of carbon for a length of subjecting the resultant product to intermittenttime sufficient to produce autogenously formed 1y applied compacting pressure while confined resinous binders as a result of the ensuing 5 between metallic heat-conducting surfaces, which thermolysis of the same.

latter are at a surface temperature of at least HARRY K. IDIZELL. 

